The invention relates to a support mechanism for a marine drive unit, such as an outboard engine or the outboard stern-drive portion of an inboard/outboard engine system, for boats, rafts and other marine vessels that permits tilting, trimming and locking of the unit. More particularly, the invention pertains to such mechanisms including fluid-pressurized apparatus for permitting various tilting, trimming and locking functions.
A typical outboard drive unit is attached to the stern of a marine vessel by means of a vertically pivotable support bracket that allows the drive unit to be selectively tilted downwardly into, or upwardly out of, the water. In order to perform satisfactorily, the drive unit should preferably be capable of being locked in its down position so that the drive unit does not swing upwardly due to the thrust of the propeller when the vessel is driven in the reverse direction. The locking system should preferably also prevent the drive unit from being swung upwardly by the resistance of the water when the vessel suddenly decelerates or stops. In order to prevent or at least minimize damage to the drive unit, however, the locking system preferably should automatically release and allow the drive unit to swing upwardly in the event of a collision with a submerged obstacle. The locking system preferably should also be selectively releasable by the operator so that the drive unit may be tilted out of the water for landing or storage.
Previous tilt-lock mechanisms typically attempt to perform some or all of the above functions by means of a multitude of interconnected linkages and springs that are inordinately complicated and expensive. Some previous tilt-lock systems, however, have substituted hydraulic, hydropneumatic, or gas-pressurized hydraulic apparatus for such linkages and springs but have either been unsuccessful in reducing the complexity and cost of the system or have been unable to adequately perform the required functions. Examples of such systems are set forth in U.S. Pat. Nos. 4,064,824; 4,052,952; 3,999,502; 3,983,835; 3,888,203; 3,863,592; 3,839,986; Re. 27,932; 3,722,455; 3,434,450; 3,434,448; and 3,285,221.
An examination of the prior art reveals that the need has arisen for a simple, inexpensive tilt-lock system for outboard drive units that is easy to operate and that adequately performs the above-discussed functions.